The long-range goal of this project is to elucidate the role of the aldehyde dehydrogenases (ALDH3A1 and ALDH1A1) in the molecular responses of the corneal epithelium to UV radiation (UVR). ALDH3A1 and ALDH1A1 represent major corneal soluble proteins in mammalian species, including human. Both ALDH3A1 and ALDH1A1 have also been identified in human lens epithelium. It is well known that UVR induces intracellular production of reactive oxygen species (ROS) that lead to increased membrane lipid peroxidation and accumulation of toxic aldehydes. Both ALDH3A1 and ALDH1A1 exhibit high substrate specificity for aldehydes produced during lipid peroxidation, which has been implicated in the pathogenesis of several diseases including cataract and degenerative retinal disease. Accumulation of malondialdehyde (MDA) and/or 4-hydroxy-2-nonenal (4-HNE), two major products of lipid peroxidation, has been observed in pathologic corneas, cataracts, and retinal disorders. Although very little is known about the role of ALDH1A1 in cornea, ALDH3A1 appears to protect the eye from UVR-induced oxidative damage. The exact molecular mechanisms by which ALDH3A1 protects the cornea and possibly the entire eye against the deleterious effects of UVR remain unclear. Corneal ALDH3A1 detoxifies peroxidic aldehydes and generates NADPH in the cytoplasm, which can function as an antioxidant directly (scavenging ROS) and/or indirectly (regenerating GSH). Both GSH depletion and lipid peroxidation are believed to have a causative role in UVR-induced eye pathologies. It has also been proposed that ALDH3A1 may scavenge ROS. A direct correlation between low ALDH expression and keratoconus has been reported. We have shown that SWR/J mice, which are sensitive to UVR, lack ALDH3A1 protein due to mutations in the structural gene. In addition, we have found that ALDH3A1 protects human corneal epithelial cells against 4-HNE- and UVR-induced cytotoxicity and apoptosis. Our working hypothesis is that ALDH3A1 and ALDH1A11 play a critical role in the cornea by disposing of UVR-generated cytotoxic aldehydes and maintaining redox balance. In the next 5 years, we therefore propose to: Specific Aim 1: Test the hypothesis that ALDH3A1 and ALDH1A1 protect corneal epithelial cells and stromal keratocytes against UVR- and 4-HNE-induced oxidative damage by metabolizing 4-HNE, thus protecting proteasomal function. Specific Aim 2: Test the hypothesis that corneal ALDH3A1 and ALDH1A1 function as: a) direct antioxidants by scavenging hydroxyl radical and reactive oxygen species; and b) indirect antioxidants by generating NADPH, NADH and GSH. Specific Aim 3: Use Aldh3a1(-/-), Aldh1a1(-/-) and Aldh3a1(-/-)/Aldh1a1(-/-) single and double transgenic knockout mouse lines to test the hypothesis that corneal ALDHs protect the eye against UVR-induced corneal injury and cataract formation.